LED chips can generally be divided into three types by structure, i.e., standard LED chip, inverted LED chip and vertical LED chip. Currently, the standard LED chip is mostly widely applied for its low fabrication method and high yield. However, it cannot meet high-power requirements from flashlight LED lamp bead of popular smart phones in recent years. Under this background, it becomes a trend to develop vertical LED chip capable of large power. In general, thanks to vertical electrode design, the power of vertical LED chip is about 1.5 times of that of the standard LED chip. However, the vertical LED chip with vertical electrode also requires a conductive substrate. In consideration of cost performance, Si substrate is a perfect choice.
In traditional vertical LED chip packaging structure with Si substrate, as shown in FIG. 1, the blue light provided by LED chip enters to the packaging glue to stimulate yellow light and the mixture of blue light and yellow light will produce white light. While the blue light enters to the packaging glue particle, the packaging glue particle only absorbs part of blue light and the remaining blue light will be refracted to the next packaging glue particle. Therefore, during a series of light mixtures, the blue light will be continuously refracted and change its optical path. Some blue light will even be refracted back to the chip. Since Si substrate will absorb all light within visible light range, including the blue light and yellow light, when the vertical LED is used in lighting system, e.g., packaged LED lamp head, it will reduce conversion efficiency from blue light to white light and reduce luminance.